1. Field of the Invention
This invention relates to laminated panes of the type known as asymmetric panes, composed of a monolithic or laminated support of glass and/or of plastics material and of at least one sheet of plastics material comprising at least one polyurethane film.
2. Discussion of the Background
Asymmetric panes are commonly used as panes for vehicles in the transportation industry, notably as windscreens for automobiles, aircraft and trains, and also in the construction industry as panes in buildings. The mounting of these panes in the window opening of an automobile body for example, by means of a profiled seal of elastic material is now generally obsolete, having been replaced by a mounting process which involves bonding the pane directly to the bodywork or window frame. Indeed, this type of mounting has advantages; notably, in the case of automobiles, it enables the windscreen to be retained in the bodywork opening despite violent impact, the mounting process can be automated and, in addition, it allows flush mounting of the pane with the vehicle body, which apart from improving the aesthetics of the vehicle, has the advantage of reducing the coefficient of penetration of the vehicle through air (drag coefficient).
In the case of the mounting of a conventional laminated pane, that is to say a pane formed of two sheets of glass and one intermediate sheet of an energy-absorbing material, such as polyvinyl butyral, the gluing of the pane onto a fold of the metal sheet of the bodywork is achieved by deposition of a suitable adhesive cord on an enamelled border disposed at the periphery of the surface of the pane which faces towards the vehicle interior, the enamelled border being intended for protecting the adhesive from ultra-violet radiation and also for concealing an inelegant adhesive seal from view.
In the case of the safety panes falling within the scope of the present invention, composed of a rigid support and at least one sheet of flexible plastics material having an external polyurethane film, when the sheet of plastics material is to fulfil the function of an energy absorber, it is necessary to glue the periphery of this sheet directly onto the frame of the vehicle body opening. A cord of suitable adhesive may be that used for gluing laminated panes of the conventional type referred to earlier. This cord is generally a two-component polyurethane or a single-component polyurethane which hardens in the presence of humidity.
When the direct bonding of the sheet of plastics material to the frame of the opening is performed with this cord, the adhesion finally obtained is not entirely satisfactory, the adhesive forces not being initially sufficient or not maintaining their strength sufficiently with time. This insufficient adhesion is due, notably, to the presence of release agents on the surface of the polyurethane film originating from the production process which involves casting the polyurethane film onto a support film of plastics material such as polyester coated with a parting agent. Such parting agents may be, for example, a product based upon silicone.